Ozone generator

ABSTRACT

An ozone generator for generating ozone by applying a specified process to oxygen by discharge includes a first raw material gas supply unit for supplying the oxygen as a first raw material gas, and a second raw material gas supply unit for supplying an oxide compound gas as a second raw material gas, in which, by excited light, excited and generated by a discharge in the oxygen and the oxide compound gas, the oxide compound gas is dissociated, or the oxide compound gas is excited accelerating dissociation of the oxygen, and ozone is generated. In this way, ozone generation efficiency is raised.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ozone generator and an ozonegenerating method, and particularly to an ozone generator which includesa high voltage electrode and a low voltage electrode, causes dischargeby the application of an AC voltage between them, and generates an ozonegas, and an ozone generating method.

2. Description of the Related Art

In the related art, various techniques as described below have beendeveloped.

JP-B-6-21010 discloses an ozone generator in which a raw material gas issupplied from a first raw material supply system for supplying aspecified flow rate of oxygen from an oxide cylinder with a purity of99.995% or more, and from a second raw material supply system forsupplying a specified flow rate of second raw material gas (nitrogen,helium, argon, or carbon dioxide) with a purity of 99.99% or more, ahigh AC voltage is applied between electrodes to cause silent discharge(dielectric barrier discharge) through a dielectric between theelectrodes, and the raw material gas is transformed into an ozone gas.The publication discloses that although the cause of a time-varyingreduction phenomenon of ozone concentration is not clear, thetime-varying reduction phenomenon exists in the ozone gas once generatedby the ozone generator under high purity oxygen, and as means forsuppressing the time-varying reduction, it is effective to add anitrogen gas or the like to the high purity oxygen.

Japanese Patent No. 2641956 discloses that a mixture ratio of an oxygengas as a raw material gas of an ozonizer to a nitrogen gas is set in arange of 1:0.0002 (200 ppm) to 0.0033 (3300 ppm). Besides, FIG. 2 ofJapanese Patent No. 2641956 shows a characteristic of the quantity ofaddition of nitrogen gas and the concentration of ozone obtained by theozonizer, and as the quantity of addition of nitrogen at whichsufficient ozone concentration (about 100 g/m³ or more) is obtained, themixture ratio is set to 1:0.0002. In order to suppress the quantity ofgeneration of nitrogen oxide as a reaction poisonous substance from theozonizer to be small, the mixture ratio is set to 1:0.0033 or less. Thepublication discloses that when the oxygen raw material gas in which thequantity of addition of nitrogen is 100 ppm or less is used, the ozoneconcentration of 20 g/m³ (9333 ppm) is merely obtained, which is ⅙ orless of the ozone concentration of 120 g/m³ (56000 ppm) at the time whenthe quantity of addition of nitrogen is 3300 ppm. Besides, in thespecification, it is disclosed that although an argon gas instead of thenitrogen gas is added to the high purity oxygen, the ozone concentrationof about 20 g/m³ (9333 ppm) is merely obtained independent of an argonmixture ratio, and the argon gas does not have an effect to raise theozone concentration.

Besides, JP-A-11-21110 discloses an ozone generator in which a TiO₂ filmis formed on a discharge surface of a dielectric. Instead of theaddition of high purity nitrogen gas, the discharge surface of thedielectric in the generator is coated with titanium oxide having a metalelement ratio of 10 wt % or more. It is disclosed that when the materialgas is supplied and the ozone gas is generated in this generator, thetime-varying reduction of ozone concentration can be prevented by thephotocatalytic action of TiO₂. In the case where a nitrogen gas is addedto high purity oxygen to stably generate ozone, nitrogen oxide (NOx) asa reaction poisonous substance is generated as a by-product of the ozonegas by silent discharge. However, it is pointed out that as means forpreventing the generation thereof, the coating of the titanium oxide iseffective.

Further, Japanese Patent No. 2587860 proposes that in an ozonizer whichcan obtain a maximum ozone concentration of 180 g/m¹³ the quantity ofaddition of nitrogen is made 0.01% to 0.5% in order to suppress thetime-varying reduction of ozone concentration.

In the related art, with respect to the mechanism of generating theozone gas by silent discharge, it is said that the ozone gas isgenerated by following reaction equations.

e+O₂

2O+e (dissociation of oxygen)  R1

O+O₂+M

O₃+M (ozone generation based on triple collision by oxygen atom andoxygen material)  R2

e+O₃

O+O₂ +e (electron collision decomposition)  R3

O₃+heat T

O+O₂ (heat decomposition)  R4

O₃+N

O₂+N1 (decomposition of ozone by impurity N)  R5

Incidentally, N1 denotes an impurity different from N.

The generation of the ozone gas is such that the oxygen molecule isdissociated to the oxygen atoms in R1, and the ozone is generated basedon the triple collision by the oxygen atom and the oxygen material inR2.

As the decomposition of the generated ozone, the electron collisiondecomposition of R3, the heat decomposition of R4, the decomposition ofozone by the impurity of R5, or the like is conceivable.

As the ozone gas which can be extracted from the generator, the ozonegas is obtained according to the balance state of the reaction equationsof R1 to R5. That is, the ozone gas can be extracted by a followingequation.

extractable ozone=(R1*R2)−(R3+R4+R5+ . . . ).

Besides, in the related art, in the case of the high purity oxygen, withrespect to the ozone generated by the ozone generation mechanism, sincethe ozone concentration is reduced with the passage of time during theoperation, the nitrogen gas is added to the raw material gas, or TiO₂ asthe photocatalyst is applied to the discharge electrode surface, so thata following reaction occurs, and the time-varying reduction of the ozoneconcentration is prevented.

O₃*+N₂

O₃

O₃*+TiO₂

O₃

JP-B-6-21010, Japanese Patent No. 2641956, and JP-A-11-21110 are forstably obtaining the ozone concentration at a relatively low ozoneconcentration of about 120 g/m³.

Besides, Japanese Patent No. 2587860 discloses to obtain an ozoneconcentration of about 180 g/m³ or less.

Incidentally, in the respective related art, different phenomena asdescribed below are described.

Although JP-B-6-21010 discloses that a gas of helium, argon, or carbondioxide is also effective as a gas other than the nitrogen gas, JapanesePatent No. 2641956 discloses that in the case of the high purity oxygen,the argon gas is not effective.

Although JP-B-6-21010 discloses that the quantity of addition of thesecond raw material gas is made 10000 ppm to 100000 ppm, Japanese PatentNo. 2641956 discloses 200 ppm to 3300 ppm which is different from theformer.

JP-B-6-21010 discloses that in the high purity oxygen, the concentrationis reduced by the operation for about one hour, while JP-A-11-21110discloses the concentration reduction after the operation for about 7hours, which is different from the former.

As described above, in the related art in which the nitrogen gas or thelike is added to the ozone generated by the apparatus in order tosuppress the time-varying reduction of the ozone concentration, theresults and effects vary according to the conditions, and althoughexperimental confirmation was made for JP-B-6-21010, Japanese Patent No.2641956 and JP-A-11-21110, JP-B-6-21010 and JP-A-11-21110 could not besubstantiated, and it turned out that addition of a separate noble gas(helium, neon, argon, xenon, etc.) other than nitrogen was ineffective.

Both JP-B-6-21010 and Japanese Patent No. 2587860 disclose that thereduction of the ozone concentration is the time-varying reduction,however, it is disclosed that when the concentration is once reduced, itdoes not return to the original ozone concentration. From the recitationthat the concentration does not return to the original ozoneconcentration, it can not be judged that the concentration reduction isthe time-varying reduction, and the role of the addition of nitrogen isnot clear.

Further, it turned out that when the nitrogen was added at an additiverate of approximately 0.15% (1500 ppm) or more, in addition to the ozonegas, a large quantity of NOx by-product gas such as N 20, or N₂O wasgenerated by the silent discharge.

N₂O₅+H₂O

2HNO₃

OH+NO₂+M

HNO₃+M

Besides, when a large quantity of NOx by-product is generated, a nitricacid (HNO₃) cluster (vapor) is generated by the reaction of the NOx gascomponent and moisture contained in the raw material gas, and theozonized gas is extracted in such a state that a trace quantity of NOxgas and nitric acid cluster, together with oxygen and ozone gas, aremixed. When the quantity of the trace quantity of nitric acid clustercontained is several hundred ppm or more, there are problems that rustof chromium oxide or the like is deposited by nitric acid on the innersurface of a stainless pipe as an ozone gas outlet pipe, a metalimpurity is mixed into a clean ozone gas, the metal impurity as areaction gas for a semiconductor manufacturing apparatus has a badinfluence on the manufacture of a semiconductor, and the trace quantityof the generated nitric acid cluster has a bad influence as a reactionpoisonous substance on “an etching process of a silicon oxide film byozone” or “ozone water washing of a wafer or the like” of asemiconductor manufacturing apparatus.

In the ozone apparatus of the related art, the concentration of theextracted ozone is low, and in order to extract ozone with a highconcentration of 200 g/m³ or more, there is only a method of increasingthe nitrogen additive rate or a method of decreasing the gas flow rate.In the method of increasing the nitrogen additive rate, as describedabove, there is a problem that the by-product gas of NOx is increased.

Besides, when the gas flow rate is decreased, there are problems thatthe quantity of ozone generation is extremely lowered, and productionefficiency on the side of using the ozone becomes worse.

Further, in the newest “etching apparatus of an oxide film by ozone” or“ozone water washing of a wafer or the like”, a high ozone concentrationof 200 g/m³ or more is needed, and with respect to the quantity of ozonegeneration, there is a request for an ozone apparatus having an ozonecapacity of several tens g/h or more on an economically viable basis inproduction on the user side, and further, in a semiconductormanufacturing apparatus, an apparatus producing less reaction poisonousmaterial such as nitric acid has been needed.

Besides, although a trace quantity, about 1%, of N₂ gas is added inorder to increase the generation efficiency of an ozone gas, the N₂ gasis transformed into NOx or nitric acid cluster by discharge in thegenerator.

Thus, there are problems that in the discharge space, as the gas flowvelocity becomes low, or the injected discharge power becomes high, thequantity of addition of nitrogen is decreased at the downstream part ofthe discharge space, a large quantity of NOx and nitric acid cluster aregenerated, the ozone generation efficiency is lowered, and theconcentration of the extracted ozone is reduced.

SUMMARY OF THE INVENTION

The invention has been made to solve the foregoing problems, and anobject thereof is to provide an ozone generator which can adequatelyraise an ozone generation efficiency.

An ozone generator of the invention includes, in an ozone generator forgenerating ozone by applying a specified process to an oxygen gas bydischarge, a first raw material gas supply unit for supplying the oxygengas as a first raw material gas, and a second raw material gas supplyunit for supplying an oxide compound gas as a second raw material gas,in which by excited light excited and generated by the discharge underexistence of the oxygen gas and the oxide compound gas, the oxidecompound gas is dissociated, or the oxide compound gas is excited tohave an accelerating action of dissociation of the oxygen gas, so thatthe ozone is generated.

According to the ozone generator of the invention, the ozone generationefficiency can be adequately raised. Especially, when a nitrogen dioxidegas is used as the oxide compound gas, as compared with a nitrogen gas,the ozone generation efficiency becomes high, and as a result, thequantity of generation of NOx by-product can be decreased.

Besides, an ozone generator of the invention includes a first electrode,a second electrode facing the first electrode to form a discharge area,a first raw material gas supply unit for supplying an oxygen gas as afirst raw material gas, a second raw material gas supply unit forsupplying a second raw material gas as an oxide compound gas or capableof generating an oxide compound gas, and a third raw material gas supplyunit for supplying a third raw material gas which is excited bydischarge and generates excited light to dissociate the oxide compoundgas or to excite the oxide compound gas to accelerate dissociation ofthe oxygen gas, wherein an AC voltage is applied between the firstelectrode and the second electrode from a power supply to injectdischarge power to the discharge area, specified quantities of the rawmaterial gases by the first to the third raw material gas supply unitsare supplied to a space where the discharge is generated between gaps ofthe discharge area, and an ozone gas is generated.

According to the ozone generator of the invention, since the thirdraw-material gas is used which is excited by the discharge and generatesthe excited light to dissociate the oxide compound gas or to excite theoxide compound gas to accelerate the dissociation of the oxygen gas, theozone generation efficiency can be adequately raised.

Besides, an ozone generator of the invention includes a first electrode,a second electrode facing the first electrode to form a discharge area,a first raw material gas supply unit for supplying an oxygen gas as afirst raw material gas, a photocatalytic material provided on adielectric in the discharge area or on the electrode and for absorbinglight in a specified wavelength range or a material transformed into aphotocatalyst by discharge, and a third raw material gas supply unit forsupplying a third raw material gas which is excited by the discharge andgenerates excited light to excite the photocatalytic material toaccelerate dissociation of the oxygen gas, wherein an AC voltage isapplied between the first electrode and the second electrode from apower supply to inject discharge power to the discharge area, specifiedquantities of the raw material gases by the first and the third rawmaterial gas supply units are supplied to a space where the discharge isgenerated between gaps of the discharge area, and an ozone gas isgenerated.

According to the ozone generator of the invention, since thephotocatalytic material or the material transformed into thephotocatalyst is used, the ozone generation efficiency can be adequatelyraised.

Further, an ozone generator of the invention includes a first electrode,a second electrode facing the first electrode to form a discharge area,a first raw material gas supply unit for supplying an oxygen gas as afirst raw material gas, a photocatalytic material provided on adielectric in the discharge area or on the electrode and for absorbinglight in a specified wavelength range or a material transformed into aphotocatalyst by discharge, a second raw material gas supply unit forsupplying a second raw material gas as an oxide compound gas or capableof generating an oxide compound gas, and a third raw material gas supplyunit for supplying a third raw material gas which is excited by thedischarge and generates excited light to excite the photocatalyticmaterial and the oxide compound gas to generate an oxygen atom, whereinan AC voltage is applied between the first electrode and the secondelectrode from a power supply to inject discharge power to the dischargearea, specified quantities of the raw material gases by the first to thethird raw material gas supply units are supplied to a space where thedischarge is generated between gaps of the discharge area, and an ozonegas is generated.

According to the ozone generator of the invention, the ozone generationefficiency can be adequately raised. Especially, since the photocatalticmaterial or the material transformed into the photocatalyst is used, andthe oxide compound gas (second raw material gas) is added to the rawmaterial gas, the oxide compound gas itself has the capacity to generatethe ozone, and the ozone can be more stably generated, and the apparatushaving a long lifetime can be obtained.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a gas system view showing an ozone generator in embodiment 1of the invention.

FIG. 2 is a schematic view showing an ozone generation mechanism in theembodiment 1.

FIG. 3 is a characteristic diagram showing an ozone concentrationcharacteristic in the embodiment 1.

FIG. 4 is a characteristic diagram showing an ozone concentrationcharacteristic in the embodiment 1.

FIG. 5 is a characteristic diagram showing an ozone concentrationcharacteristic in the embodiment 1.

FIG. 6 is a characteristic diagram showing an ozone concentrationcharacteristic in the embodiment 1 and is an enlarged characteristicdiagram of FIG. 5.

FIGS. 7A and 7B are characteristic diagrams showing a relation of aconcentration of generated ozone with respect to an additive rate ofnitrogen dioxide in the embodiment 1.

FIG. 8 is a characteristic diagram showing a generation ratio ofnitrogen dioxide by discharge in a case where a nitrogen gas is added inthe embodiment 1.

FIG. 9 is a gas system diagram showing an ozone generator of embodiment2.

FIG. 10 is a gas system diagram showing an ozone generator of embodiment3.

FIG. 11 is a gas system diagram showing an ozone generator of embodiment4.

FIG. 12 is a gas system diagram showing an ozone generator of embodiment5.

FIG. 13 is a gas system diagram showing an ozone generator of embodiment6.

FIG. 14 is a gas system diagram showing an ozone generator of embodiment7.

FIG. 15 is a gas system diagram showing an ozone generator of embodiment8.

FIG. 16 is a gas system diagram showing an ozone generator of embodiment9.

FIG. 17 is a gas system diagram showing an ozone generator of embodiment10.

FIG. 18 is a gas system diagram showing an ozone generator of embodiment11.

FIG. 19 is a characteristic diagram showing an ozone concentrationcharacteristic according to existence of a photocataltic material ofthis invention.

FIG. 20 is a characteristic diagram showing an ozone concentrationcharacteristic with respect to the quantity of nitrogen dioxide or thequantity of nitrogen of this invention.

FIG. 21 is a characteristic diagram showing an ozone reactioncharacteristic with respect to an ozone concentration of this invention.

FIG. 22 is a characteristic diagram showing an ozone water concentrationwith respect to an ozone concentration of this invention.

FIG. 23 is a structural view for explaining an ozone generator of thisinvention.

FIG. 24 is a characteristic diagram showing an ozone concentrationcharacteristic for explaining this invention.

FIG. 25 is a characteristic diagram showing an ozone concentrationcharacteristic for explaining this invention.

FIG. 26 is a characteristic diagram showing a discharge power density ata nitrogen additive rate of 0.1% and an ozone concentration reductionrate in this invention.

FIG. 27 is a characteristic diagram showing an ozone concentrationcharacteristic with respect to W/Q in this invention.

FIG. 28 is a characteristic diagram showing a characteristic of an ozonegeneration efficiency η (mg/J) with respect to a nitrogen additive rateγ in this invention.

FIG. 29 is a characteristic diagram showing a light wavelength and anenergy absorption coefficient of an oxygen molecule, at which an oxygengas can be dissociated.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

Embodiment 1 of this invention will be described with reference to FIGS.1 to 8. FIG. 1 is a block diagram showing a structure of a gas system inthe embodiment 1. FIG. 2 is a schematic view showing an ozone generationmechanism in the embodiment 1. FIGS. 3 to 8 are diagrams showing ozoneconcentration characteristics in the embodiment 1.

An ozone generator of this invention is effective when used in a caserequiring a high concentration ozone gas of 200 g/m³ or more, a cleanozone gas as in a semiconductor manufacturing apparatus or a washingapparatus, an ozone gas in which a by-product such as NOx is suppressed,or an apparatus having a high ozone generation efficiency.

In FIG. 1, a type A raw material supply system 100 for supplying a gasin which oxygen (first raw material gas) having a purity of 99.99% ismixed with a trace quantity of nitrogen or nitrogen dioxide N 204 (NO₂)(second raw material gas), is constituted by a high purity oxygencylinder 10, a nitrogen or oxide compound gas (second raw material gas)cylinder 12, pressure reducing valves 13 and 14 for the respectivecylinders, and open/close valves 15 and 16, and a second raw materialgas 18 of 5 ppm was supplied to an oxygen gas 17.

A type B raw material supply system 200 for supplying a specifiedquantity of third raw material gas having a purity of 99.99% or more isconstituted by a high purity noble gas cylinder 20, a pressure reducingvalve 21, and an open/close valve 22, and a third raw material gas 25 bof 500 ppm or more was supplied to the oxygen gas 17.

A raw material gas 25 is supplied to an ozone generator 300 through aflow controller (MFC) 19 for controlling the gas quantities of the firstraw material gas and the second raw material gas and a flow controller(MFC) 23 for controlling the quantity of the third raw material gas.

The ozone generator 300 is provided with electrodes 301 a and 301 b anddielectrics 302. The ozone generator 300 is designed such that the rawmaterial gas 25 is supplied from the type A raw material supply systemand the type B raw material supply system, is transformed into an ozonegas 26, and is outputted to the outside through a pressure controller(APC) 400.

An ozone power supply 500 for generating ozone in the ozone generator300 is mainly constituted by a converter part 501, an inverter part 502and a transformer part 503, and applies a high AC voltage between theelectrodes 301 a and 301 b of the ozone generator 300 to generate silentdischarge (dielectric barrier discharge) through the dielectric betweenthe electrodes, and the raw material gas is transformed into the ozonegas.

Besides, although the ozone generator 300 includes a cooling unit usingwater or the like for cooling the electrodes, here, the cooling unit isomitted in the illustration.

A discharge power of up to about 2000 W is injected from the ozone powersupply to the ozone generator 300 of a type in which a both-sidedelectrode can be cooled and which is constructed with a gap length of0.1 mm and a discharge area of about 750 cm², and the raw material gas25 to be injected to the ozone generator 300 is prepared such that thenoble gas, such as argon, or the carbon dioxide gas 25 b is added fromthe third raw material gas cylinder 20 to the raw material gas 25 a inwhich the nitrogen or nitrogen dioxide NO₂ gas 18 of 5 ppm as the secondraw material gas is mixed to the oxygen gas 17 (first raw material gas)having a purity of 99.99% or more. The ozone concentrationcharacteristic with respect to the nitrogen additive rate under theabove condition was measured.

In the above setting condition of the generator, as an allowableperformance evaluation standard, the following design standard is set.

To be capable of extracting the ozone gas with an ozone concentration Cof 200 g/m³ (93333 ppm) or more by a discharge power of 2 kW and a rawmaterial gas of 10 L/min.

That is, to be capable of obtaining an ozone generation quantity Y (g/h)of 120 g/h or more under the above condition.

For that purpose, an actually extracted ozone yield X (g/kWh) is need tobe a value mentioned below or more.

X=(120 g/h)/(2 kW)=60 g/kWh

When the ratio of an ozone yield Xo of the ozone generator itself to theactually extracted ozone yield X is made 50%, the ozone yield Xo of theozone generator itself is need to be 120 g/kWh or more.

For that purpose, an ozone generation efficiency η (mg/J) is calculatedas follows.

η=(120 g/kWh)/(60·60S)/1000

=0.033 (mg/J)

The ozone generation efficiency η of 0.033 mg/J or more is needed.

This value is made an allowable standard of one apparatus, and is made aselection standard of an ozone generator and a raw material gas.

In the case where a nitrogen dioxide NO₂ gas is not mixed, in order tosatisfy the condition of the ozone generation efficiency η of 0.033 to0.035 mg/J or more, the nitrogen additive rate γ of about 1.5% or moreis needed as indicated by a characteristic 2800A of FIG. 28.

On the other hand, it has been understood that as shown in FIG. 3, whena noble gas, such as argon or xenon, of 500 ppm as the third rawmaterial gas is added to high purity oxygen of 3 SLM, and nitrogen ofapproximately 10 ppm to 500 ppm is added, the ozone generationefficiency with respect to the nitrogen additive rate γ is increased,and the ozone concentration equal to or higher than the ozoneconcentration characteristic of the case where only nitrogen gas isadded, can be extracted (incidentally, the unit “SLM” means standardL/min, and indicates L/m at 20° C.).

Besides, it has been understood that when nitrogen dioxide instead ofthe nitrogen gas of the second raw material gas is added, and argon gasof 500 ppm or more is added, the ozone generation efficiency n isincreased, and ozone with a high concentration of 200 g/m³ or more canbe obtained.

As a result, the generation quantity of NOx, such as N₂O₅ or NO, as theby-product by the discharge is lowered, a nitric acid (HNO₃) cluster bythe bonding of NOx and moisture can be decreased, and the generationquantity of metal impurity by the stainless metal surface of an ozoneoutlet pipe part and nitric acid is lowered.

FIG. 4 shows an ozone concentration characteristic in a case where a rawmaterial gas is prepared by adding nitrogen dioxide of 5 ppm as thesecond raw material gas to the oxygen gas, and by adding an argon gas of1% as the third raw material gas.

FIG. 4 shows the ozone concentration characteristic with respect to adischarge power W/Q injected per unit flow rate, and a characteristic4000A indicates a characteristic in a case where NO₂ of 5 ppm and argongas of 1% are added. Besides, a characteristic 4000B of a broken lineindicates a characteristic in a case where a nitrogen additive rate is1%. In the characteristic 4000A, when an oxide compound gas instead ofnitrogen is mixed from the first, and the argon gas of about 1% insteadof the nitrogen gas is added, a tangential line as an ozone generationefficiency η becomes large, and the ozone concentration characteristiccan be improved. However, the final ozone concentration is eventuallysaturated at 300 g/m³, irrespective of a gaseous species.

Besides, in order to raise the final ozone concentration, when theelectrode temperature of the ozone generator is lowered from 20° C. to10° C. and 5° C., ozone with a high concentration of 350 g/m³ and 400g/m³ can be extracted.

In the drawing, a point A indicates that the W/Q value at which ozone of200 g/m³ is obtained in a case of nitrogen addition quantity of 1%, isrequired to be 175 or more, and a point B indicates that the W/Q valueat which ozone of 200 g/m³ is obtained in a case of NO₂ of 5 ppm and Arof 1%, is required to be 120 or more.

That is, when the gas flow rate is constant, in the case of NO₂ of 5 ppmand Ar of 1%, the discharge power becomes 0.69 (=120/175) times as highas that of the case of N₂ of 1%, the output voltage, current and powerof the power supply are decreased, the ozone generator and the powersupply become compact, and the ozone efficiency is also increased.

FIGS. 5 and 6 show ozone concentration characteristics in a case where araw material gas is prepared by adding nitrogen dioxide to an oxygengas, and a case where a raw material gas is prepared by adding nitrogengas to an oxygen gas. The drawings show the respective ozoneconcentration characteristics with respect to discharge power W/Qinjected per unit flow rate. In the case where the nitrogen dioxide isadded, the drawings show the characteristics in the cases where nitrogendioxide of 278 ppm (characteristic 5001A), 9.2 ppm (characteristic5001B) and 6.4 ppm (characteristic 5001C) are added to the oxygen gas.Besides, a characteristic 5002A, a characteristic 5002B and acharacteristic 5002C of broken lines indicate the characteristics in thecases where nitrogen of 10000 ppm, 1000 ppm and 100 ppm are added. FIG.6 is a view enlarging the ozone concentration characteristics of FIG. 5.From the drawings, it has been turned out that when the nitrogen dioxideof several ppm is added, performance equivalent to the case where thenitrogen gas of 1% (10000 ppm) is added can be obtained, and the ozoneconcentration of 200 g/m³ or more can be secured.

From the results of FIGS. 5 and 6 of this text, the performanceequivalent to the maximum ozone concentration characteristic of the casewhere nitrogen is added can be obtained by merely adding the tracequantity of nitrogen dioxide, and therefore, it has been found that thegeneration of ozone is caused by the nitrogen dioxide more strongly thanthe nitrogen gas.

Besides, since ozone with an ozone concentration of 200 g/m³ (140000ppm) is generated by addition of nitrogen dioxide of several ppm, anozone generation magnification of the nitrogen dioxide is a factor ofhundreds of thousands [=(140000 ppm of ozone)/(1 ppm of nitrogendioxide)] and the ozone can be generated at the extremely highmagnification, and therefore, it has been found that the nitrogendioxide functions as a catalyst for the ozone generation.

Besides, when the ozone generation characteristic in the case of thenitrogen addition is compared with that in the case of the nitrogendioxide addition, the nitrogen dioxide has a capacity about 10000 timesas the ozone generation capacity of the nitrogen gas.

In FIG. 6, when the ozone concentration characteristic (5002A) of thecase where nitrogen with an additive rate of 1% (10000 ppm) is added, iscompared with the ozone concentration characteristics (5001A), (5001B)and (5001C) of the cases where nitrogen dioxides of 278 ppm, 9.2 ppm and6.4 ppm are added, as the discharge power becomes low, thecharacteristic 5002A of the nitrogen addition approaches thecharacteristic (5001C) of the case of the nitrogen dioxide of 6.4 PPM.

From these measurement facts, it can be ascertained that the ozonegeneration capacity of the nitrogen gas is not obtained by the nitrogenitself, the nitrogen gas is dissociated by silent discharge, and thenitrogen dioxide is generated so that the ozone is generated.

FIG. 8 shows the generation quantity of the nitrogen dioxide bydischarge in the case where the nitrogen gas is added, which is obtainedby performing the inverse operation from the ozone performancecharacteristic under the condition of a discharge power of 2.1 kW. FromFIG. 8, it has been clarified that the generation quantity is about 15ppm at the discharge power of 2.1 kW.

FIGS. 7A and 7B are views in which a measurement is made on the relationbetween the additive rate of nitrogen dioxide at the raw material gasflow rate of 5 L/min and the concentration of ozone which can begenerated.

In the drawings, FIG. 7A is a characteristic diagram showing thequantity of addition of nitrogen dioxide in linear display, and FIG. 7Bis a characteristic diagram showing the same in logarithmic display.

From the drawing, it has been understood that in order to obtain theozone with an ozone concentration of 200 g/m³ or more, it is sufficientif the nitrogen dioxide of 0.7 ppm or more exists. The ozoneconcentration is saturated at several tens ppm.

Besides, it has been understood that in order to obtain the ozone withan ozone concentration of 10 g/m³ (4667 ppm) or more, it is sufficientif the nitrogen dioxide of 0.2 ppb (0.0002 ppm) or more exists.

Here, although the characteristics in the case where the nitrogendioxide instead of the nitrogen gas is added, are shown, even when anitrogen monoxide gas is added, since the nitrogen monoxide has a highbonding force to oxygen as the raw material gas by discharge, and thenitrogen monoxide is transformed into nitrogen dioxide, ozone can begenerated under the addition quantity almost equal to the additionquantity of the nitrogen dioxide.

As a result of the examination of these examples, a chemical reactionprocess by the discharge of a raw material gas, the wavelength ofexcited light by the discharge of a material, a photochemical reactionof the excited light, and the like, it has been understood that ozonecan be generated by a novel ozone generation mechanism.

The oxide compound gas such as nitrogen dioxide has a thermal catalyticreaction function by a circulation reaction cycle in which the oxidecompound gas is dissociated into an oxygen atom and a suboxide such asnitrogen monoxide by excited light, and the dissociated suboxide isregenerated to the oxide compound gas by a series of chemical reactions,and a photocatalytic reaction function in which the oxide compound gasabsorbs excited light, so that the oxide compound gas itself acceleratesthe dissociation of the oxygen gas.

With respect to the ozone generation mechanism in the thermal catalyticreaction function and the photocatalytic reaction function of the oxidecompound gas of this invention, nitrogen dioxide as an example of theoxide compound gas is used as an example, and an ozone generationoperation and function will be described with reference to the schematicview of FIG. 2.

First, as shown in FIG. 29, an oxygen molecule has a light absorptionspectrum (wavelength of ultraviolet rays of 130 to 200 nm) of acontinuous spectrum at the wavelength of ultraviolet light of 245 nm orless, and it is known in an excimer lamp or the like emittingultraviolet rays that the oxygen molecule absorbs excimer light ofultraviolet light of 245 nm or less, so that it is dissociated intooxygen atoms, and ozone is generated by triple collision (reactionequation R2) of the dissociated oxygen atom, the oxygen molecule and athird material. However, like the ozone generator, in the silentdischarge in the oxygen gas as a main component and under a highpressure of 1 atom or more, excimer light of ultraviolet light of 245 nmor less is not emitted at all. Thus, dissociation of an oxygen atom bysilent discharge light and a reaction process of ozone generation arenot conceivable.

In FIG. 2, only reactions relating to the ozone generation in the silentdischarge are enumerated. First, the operation and function of thethermal catalytic chemical reaction function of the oxide compound gaswill be described. A reaction 303 indicates a reaction in which anoxygen molecule and a nitrogen molecule collide with each other in thedischarge and nitrogen dioxide or the like is generated.

A reaction 304 indicates a reaction in which a gas atom or a gasmolecule of the third raw material gas becomes an excited gas Ar* by thedischarge. The excited third raw material gas emits excited light h ν,and is returned to the ground atom.

A reaction 305 indicates a reaction in which an oxide compound moleculegenerated by the reaction 303 is dissociated by the excited lightemitted from the reaction 304, and is decomposed into an oxygen atom anda suboxide compound.

Besides, the dissociated suboxide compound (nitrogen monoxide NO) reactswith an HO₂ radical or the like generated from moisture contained in theraw material gas, is immediately returned to nitrogen dioxide NO₂, andcontributes to next oxygen atom dissociation. That is, a trace quantityof moisture performs a catalytic action of the nitrogen dioxide, and thenitrogen dioxide NO₂ functions as the thermal catalytic chemicalreaction action for dissociating the oxygen atom.

Next, the operation and action of the photocatalytic reaction functionof the oxide compound gas will be described.

In an energy level band of an oxide compound gas such as nitrogendioxide, a band gap energy between a valence band and a conduction band(forbidden band) is several eV, and when light equivalent to the bandgap energy is absorbed, the oxide compound gas itself is photoexcited,an electron escapes from the valence band and a positive hole (hole)state (excited state) occurs. When an oxygen molecule attaches to theoxide compound gas of the excited state, transfer of energy equivalentto light (ultraviolet rays of 130 nm to 200 nm) which can dissociate theoxygen gas is performed when the excited state is returned to the groundstate, and the oxygen gas is dissociated, so that the oxygen atom isgenerated. The oxide compound gas returned to the ground state is againexcited by the light of the discharge, and serves to dissociate theoxygen gas. The photocatalytic action by the oxide compound gas and theexcited light as stated above functions to increase the oxygen atoms.

An ozone generation reaction 306 by the oxygen atom indicates a reactionin which energy transfer is performed by triple collision of the oxygenatom generated at the reaction 305, the oxygen molecule, and a thirdmaterial, and an ozone molecule is generated.

Next, a description will be given of an inhibition against anaccelerating action of generation of an oxygen atom by the thermalcatalytic chemical reaction function and the photocatalytic reactionfunction of the oxide compound gas, and the operation and action ofdecomposition of generated ozone. As another discharge reaction,nitrogen dioxide (oxide compound) and nitrogen gas generate N₂O₅ gas bya binding reaction of an oxygen gas and a generated ozone molecule, andthere is also a reaction in which NOx gas such as N₂O gas is generatedby a nitrogen gas and an ozone atom. Further, a reaction 307 shows areaction in which energy transfer is performed by triple collision of anOH radical molecule from a trace quantity of oxygen in a gas, nitrogendioxide and third material, and a nitric acid cluster is generated. Theozonized oxygen 26 also includes the NOx gas and the nitric acid cluster(vapor) gas by the foregoing reaction. When the quantity of NOx and thequantity of the nitric acid cluster are increased, the quantities of thenitrogen dioxide (oxide compound) and the nitrogen gas dissociating theoxygen gas are decreased, and the action of lowering the efficiency ofozone generation is performed. The quantity of NOx other than thenitrogen dioxide is rapidly increased as the discharge power isincreased and the ozone concentration becomes high, which causes theozone concentration characteristic with respect to the discharge powerW/Q injected per unit flow rate to exhibit the saturationcharacteristic. Accordingly, in the case where the nitrogen gas isadded, when the discharge power is increased, the quantity of the NOxgas, such as the N₂O₅ gas or N2O gas, and the quantity of the nitricacid cluster, rather than the generation quantity of the nitrogendioxide, are increased by discharge, and accordingly, there is atendency that the ozone concentration characteristic is saturated at alow ozone concentration. Thus, when the nitrogen dioxide as the mainfactor of generating the ozone is added to the oxygen gas, highconcentration ozone is obtained as compared with the case where thenitrogen gas is added to the raw material gas.

Besides, with respect to the generated ozone, as the discharge powerbecomes high, the discharge power density becomes high, and the gastemperature in the discharge becomes high, and further, as theconcentration of the generated ozone becomes high, the thermaldecomposition reaction of the ozone becomes large, which causes theozone concentration characteristic with respect to the discharge powerW/Q injected per unit flow rate to show the saturation characteristic.

The ozonized oxygen 26 is extracted by a series of reactions in thedischarge, such as the dissociation reaction of the oxygen atom by theoxide compound gas and the excited light, the catalytic reaction of theoxide compound gas, ozone generation loss by transformation of the oxidecompound gas into another oxide compound gas, the thermal decompositionreaction of ozone, and ozone generation by the triple collision reactionof the oxygen atom and the oxygen gas.

From the above ozone generation mechanism, in case only high purityoxygen is used, since ozone generation by silent discharge is hardlyperformed, for the purpose of accelerating the dissociation of theoxygen by the thermal catalytic chemical reaction or the photocatalyticreaction through the high purity oxygen (first raw material gas), theexcited light and the oxide compound gas, a trace quantity of nitrogengas or nitrogen dioxide NO₂ gas is added as the second raw material gas,and further, a trace quantity of third raw material gas such as a noblegas is added, so that the raw material gas is prepared. From thenitrogen gas as the second raw material gas, the nitrogen dioxide isgenerated by discharge at the reaction 303 with the oxygen gas.

As compared with the oxygen molecule, the generated nitrogen dioxide hasa continuous absorption spectrum in which the oxygen atom can bedissociated by ultraviolet light of a long wavelength, and thewavelength of the ultraviolet light is about 300 nm to 400 nm. Thenitrogen dioxide has an absorption spectrum band at wavelengths longerthan the ultraviolet light capable of dissociating the oxygen molecule.

Thus, when a trace quantity of noble gas Ar as the third raw materialgas is added, argon emits excited light close to a wavelength of 300 nmfrom the noble gas Ar by silent discharge. By the reaction of theexcited light and the nitrogen dioxide, the nitrogen dioxide isdissociated into an oxygen atom and a nitrogen monoxide NO, and ozone isgenerated by the triple collision (reaction equation R2) of the oxygenatom, the oxygen molecule and a third material.

Besides, this dissociated nitrogen monoxide NO reacts with an HO₂radical generated from moisture contained in the raw material gas, isimmediately returned to nitrogen dioxide NO₂, and contributes to nextoxygen atom dissociation.

That is, a trace quantity of moisture performs a catalytic action of thenitrogen dioxide, and the nitrogen dioxide NO₂ functions as the thermalcatalytic chemical reaction action for dissociating the oxygen atom, andcontributes to the generation of ozone O₃. Besides, the nitrogen dioxideabsorbs the excited light, so that the oxygen atoms are increased by thephotocatalytic reaction of dissociating the oxygen gas coming in contactwith the nitrogen dioxide, and the nitrogen dioxide contributes to theefficient generation of ozone.

In the apparatus of FIG. 1, the addition quantities of the second andthe third raw material gases from the second raw material gas cylinder12 and the third raw material gas cylinder 20 can also be controlled inaccordance with an ozone concentration or a request from the user side.In a process not requesting clean ozone in the ozone gas much, thequantity of the second raw material gas is increased to generate higherconcentration ozone, and in the case where clean ozone is requested inorder to form an oxide film by CVD or the like, the second raw materialgas is decreased, the quantity of the noble gas as the third rawmaterial gas is increased, and a control is performed to achieve a modein which ozone of the highest possible concentration can be extracted.

Besides, in the embodiment 1, the raw material gas, containing theoxygen gas, of 2 L/min or more is supplied, so that the highconcentration ozone with a concentration of 200 g/m³ or more can beextracted at an ozone generation quantity of 24 g/h or more, andtherefore, the ozone generator can be obtained in which the ozonegeneration efficiency can be adequately raised, and the highconcentration ozone can be certainly obtained.

Embodiment 2

Embodiment 2 of this invention will be described with reference to FIG.9. FIG. 9 is a block diagram showing a structure of a gas system in theembodiment 2.

In the embodiment 2, the details of a structure and the details of amethod other than a specific structure and method described here are thesame as the structure and method of the embodiment 1 described before,and the same operation is achieved. Incidentally, also in embodiments 3to 11 described later, the details of a structure and the details of amethod other than a specific structure and method are the same as theembodiment 1. In the respective drawings, the same symbols denote theidentical or equivalent portions.

Although the three kinds of raw material gases are mixed in theembodiment 1, in the second embodiment, a raw material gas cylinder isconstituted by two cylinders of an oxygen cylinder 10 and a nitrogendioxide cylinder, and this embodiment is advantageous in the cost of anapparatus and its operation.

In FIG. 9, a trace quantity of nitrogen dioxide N₂O₄ (NO₂) (about 0.7ppm to 10 ppm) is added from a cylinder 12 to oxygen (first raw materialgas) having a purity of 99.99% or more supplied from the high purityoxygen gas cylinder 10, and these gases are supplied as a raw materialgas 25 to an ozone generator 300. It is preferable that an additive rateof nitrogen dioxide N₂O₄ (NO₂) is from 0.0002 ppm to several tens ppmwith respect to the oxygen gas as shown in FIG. 7. The other structureis the same as FIG. 1 of the embodiment 1.

In this embodiment 2, although the one kind of gas of the cylinder 12,that is, the trace quantity of nitrogen dioxide N₂O₄ (NO₂) is added tothe oxygen gas of the oxygen gas cylinder 10, the nitrogen dioxide N 20gas itself becomes a nitrogen atom by silent discharge, and also becomesan oxide compound gas, and this gas can also emit ultraviolet rays of300 nm as the discharge excited light.

Thus, there is an effect that the addition of only one kind of gasfunctions as both the second raw material gas and the third raw materialgas, and an ozone gas can be effectively generated. When the nitrogendioxide is directly added to the oxygen gas, the ozone generationefficiency becomes higher than that of the case where nitrogen is added,and as a result, there is an effect that the generation quantity of NOxby-product can be made extremely small. Besides, since only one kind ofgas is added to the oxygen gas, there is a merit that the equipment canbe easily formed. As the oxide compound gas to be added, nitrogenmonoxide, carbon dioxide, or carbon monoxide is effective in addition tonitrogen dioxide.

The ozone generator of the second embodiment includes, in the ozonegenerator for generating ozone by applying a specified process to anoxygen gas by discharge, the first raw material gas supply unit 10 forsupplying the oxygen gas as the first raw material gas, and the secondraw material gas supply unit 12 for supplying the oxide compound gas asthe second raw material gas, in which by excited light excited andgenerated by the discharge under existence of the oxygen gas and theoxide compound gas, the oxide compound gas is dissociated, or the oxidecompound gas is excited to have an accelerating action of dissociationof the oxygen gas, so that the ozone is generated, and therefore, theozone generator can be obtained in which the kind of added gas issimplified, and the ozone generation efficiency can be adequatelyraised.

Besides, according to the embodiment 2, in the above structure, as aunit for changing the ozone concentration or ozone generation quantity,a variable unit including a flow controller (MFC) 23 capable of changingthe additive rate of the nitride dioxide gas to the oxygen gas isprovided, so that the ozone generator can be obtained in which the ozonegeneration efficiency can be more adequately raised.

Embodiment 3

Embodiment 3 of this invention will be describe d with reference to FIG.10. FIG. 10 is a block diagram showing a structure of a gas system ofthe embodiment 3.

In FIG. 10, a first and second raw material mixture gas in which a tracequantity of nitrogen or nitrogen dioxide N₂O₄ (NO₂) (second raw materialgas) is mixed to oxygen (first raw material gas) having a purity of99.99%, is supplied from a first and second raw material mixture gasdedicated gas cylinder 101, and a noble gas such as argon is suppliedfrom a cylinder 20.

In the embodiment 3, it has been experimentally confirmed that even ifnitrogen dioxide NO₂ or nitrogen monoxide NO instead of nitrogen ismixed, nitrogen dioxide is generated by the reaction of reactionequations R71 and R81 (described later) in a discharge space part, andthe ozone generation efficiency η is increased.

According to the embodiment 3, in the structure of the embodiment 1 orthe embodiment 2, as a dedicated raw material gas cylinder forgenerating the ozone, the dedicated raw material gas cylinder 101 isconstructed which contains the oxygen gas as the first raw material gasand the oxide compound gas as the second raw material gas or a tracequantity of nitrogen capable of generating nitrogen dioxide N₂O₄ (NO₂)or the oxide compound gas, so that the ozone generator capable ofadequately raising the ozone generation efficiency can be obtained bythe simple raw material supply structure.

Embodiment 4

Embodiment 4 of this invention will be described with reference to FIG.11. FIG. 11 is a block diagram showing a structure of a gas system ofthe embodiment 4.

In FIG. 11, a gas in which oxygen and an oxide compound gas such as anitrogen dioxide gas are mixed, is supplied from an oxygen (first rawmaterial gas) cylinder 102 containing oxygen with a purity of 99.99% andfrom an auxiliary gas cylinder 2000 in which a trace quantity ofnitrogen monoxide or nitrogen dioxide N₂O₄ (NO₂) (second raw materialgas) is mixed with a noble gas (helium, neon, argon, xenon, etc.). Theother structure is the same as FIG. 1 in the embodiment 1.

In the embodiment 4, it has been experimentally confirmed that even ifnitrogen monoxide NO instead of nitrogen dioxide is mixed, since thenitrogen dioxide is very quickly generated from the nitrogen monoxide NOby the chemical reaction of the reaction equations R71 and R81 in adischarge space part, the ozone generation efficiency η equal to thecase where the nitrogen dioxide is added can be obtained.

According to the embodiment 4, in the structure of the embodiment 1 orthe embodiment 2, with respect to the relevance between the nitrogendioxide and the concentration performance of ozone which can begenerated in the generator, as shown in FIG. 7, the sufficientperformance can be obtained by merely adding a trace quantity ofnitrogen dioxide NO₂, the addition quantity of which is from 0.7 ppm to10 ppm.

However, as in the embodiments 1 and 2, it is very difficult to obtain asingle nitrogen dioxide cylinder in view of the safety and refining ofthe cylinder.

Besides, as in the embodiment 3, when the dedicated cylinder in whichthe nitrogen dioxide is added to the oxygen is made, since the quantityof the nitrogen dioxide is very small, when the oxygen cylinder is madein which a predetermined quantity of nitrogen dioxide is added, the veryexpensive cylinder needs to be supplied. Besides, it has been understoodthat when the nitrogen dioxide is added to the main raw material gas(oxygen) for generating ozone, the oxygen gas in which the nitrogendioxide is added, is consumed in proportion to the quantity of thesupplied oxygen gas, and the cost of the raw material gas becomes veryhigh.

The embodiment 4 has been made to solve the problems of the embodiments1, 2 and 3.

That is, a unit for obtaining a raw material gas which is added withnitrogen dioxide of about 5 ppm and is supplied to an ozone generator,is constructed as follows.

The auxiliary cylinder 2000 is obtained by adding nitrogen dioxide ofseveral tens (ppm) to thousands ppm, the addition of which is easy, to anoble gas as a third raw material gas, and a unit is formed which mixesand supplies the noble gas added with the oxide compound gas such asnitrogen dioxide from the auxiliary cylinder 2000 in a range of about0.1% to several % to the oxygen gas as the first raw material gas fromthe oxygen cylinder 102. As a result, the oxide compound gas, such asthe nitrogen dioxide, as the second raw material gas can be mixed to theoxygen gas at the order of ppm, and the oxygen gas 25 in which the thirdraw material gas of from several hundred ppm to several tens ofthousands ppm is also added can be supplied to the ozone generator.

As described above, when the auxiliary raw material gas cylinder 2000 isformed in which the oxide compound gas is added to the noble gas, theozone performance is sufficiently secured, and the relativelyinexpensive auxiliary raw material gas cylinder 2000 can be provided.

Besides, the consumption of gas quantity of several % or less issufficient for the consumption of the oxygen gas as the main gas, andthere is an effect that running cost can be greatly reduced.

Further, since the addition quantity of the oxide compound gas to theoxygen raw material gas can be easily made variable by arbitrarilychanging the gas quantity from the auxiliary gas cylinder, there is aneffect that the ozone performance can be controlled in a specifiedrange.

Incidentally, in the case where nitrogen is added to the oxygen gas,nitrogen dioxide must be generated once by discharge, and the quantityof the generated nitrogen dioxide is varied by the state of silentdischarge and the discharge power. Thus, the generation quantity of highconcentration ozone is not stably obtained so that a large quantity ofnitrogen gas must be added. On the other hand, when the nitrogen dioxideas the main factor to generate ozone is added to the raw material gas,ozone stabler than that in the case of the addition of the nitrogen gasis obtained.

Embodiment 5

Embodiment 5 of this invention will be described with reference to FIG.12. FIG. 12 is a block diagram showing a structure of a gas system inthe embodiment 5.

In FIG. 12, a first and third raw material mixture gas in which a tracequantity of noble gas (third raw material gas) is mixed to oxygen (firstraw material gas) having a purity of 99.99% or more is supplied from afirst and third raw material mixture gas dedicated gas cylinder 102, anda nitrogen gas is supplied from a cylinder 12.

In the dedicated gas cylinder in which the noble gas is mixed to oxygen,even if the addition quantity of the noble gas is made 0.5% or more, abad influence to increase a by-product gas such as NOx in an ozonegenerator does not occur, and therefore, the dedicated gas cylinder canbe inexpensively formed.

The other structure is equivalent to the structure of FIG. 1 in theembodiment 1. Also in this structure, the ozone concentration equivalentto the embodiment 1 can be obtained.

According to the embodiment 5, in the structure of the embodiment 1 orthe embodiment 2, as the dedicated raw material gas cylinder forgenerating the ozone, the first and third mixture gas dedicated rawmaterial gas cylinder 102 is constructed which supplies the first andthird mixture gas in which the gas made of the trace quantity of noblegas as the third raw material gas is made to be contained in the oxygengas as the first raw material gas, and the nitrogen gas as the secondraw material gas is supplied from the cylinder 12, so that the ozonegenerator can be obtained in which the ozone generation efficiency canbe adequately raised by the simple raw material supply structure.

Embodiment 6

Embodiment 6 of this invention will be described with reference to FIG.13. FIG. 13 is a block diagram showing a structure of a gas system inthe embodiment 6.

In FIG. 13, a first and third raw material gas in which a trace quantityof noble gas (third raw material gas) is mixed to oxygen (first rawmaterial gas) having a purity of 99.99% or more is supplied from a firstand third raw material gas dedicated gas cylinder 102, and carbondioxide CO₂ or carbon monoxide CO gas (second raw material gas) issupplied from a cylinder 12A.

Since the N₂ gas or nitrogen dioxide gas is not added, the ozonegenerator can be obtained in which a by-product such as NOx is notgenerated at all. The other structure is the same as FIG. 1 in theembodiment 1.

In the embodiment 4, even if carbon dioxide Co 2 or carbon monoxide COinstead of nitrogen dioxide is mixed as the second raw material gas,similarly to the oxygen atom by ultraviolet light of NO₂, in thefollowing reaction equations, the CO₂ gas also causes the oxygen atomdissociation by light or accelerates the dissociation of the oxygen gasby the photocatalyst of the oxide compound gas, and it has beenexperimentally confirmed that also in the carbon dioxide, the ozonegeneration efficiency η is increased although the generation efficiencyis worse than nitrogen dioxide.

CO₂ +hν

CO+O(³P)  R6

H+O₂+M

HO₂+M  R7

HO₂+CO

OH+CO₂  R8

O(³P)+O₂+M

O₃+M  R2

That is explained as follows. An oxygen atom O(³P) is formed (reactionof R6) by carbon dioxide CO₂ and ultraviolet light in the vicinity of300 nm by excitation of the noble gas, and ozone is generated (reactionof R₂) by triple collision of the generated oxygen atom O(³P) and anoxygen molecule O₂. Carbon monoxide CO generated by the reaction of R6reacts with an HO₂ radical generated by the reaction of R7, and carbondioxide CO₂ is regenerated (reaction of R8).

That is, during a time when the raw material gas passes through thesilent discharge space, the carbon dioxide CO₂ repeats the reactioncycle of R6→R7→R8→R6 and is regenerated.

According to the embodiment 6, in the structure of the embodiment 1, 2,3, 4 or 5, as the dedicated raw material gas cylinder for generating theozone, the first and third mixture gas dedicated raw material gascylinder 102 is constructed which supplies the first and third mixturegas in which the gas made of the trace quantity of noble gas as thethird raw material gas is made to be contained in the oxygen gas as thefirst raw material gas, and the carbon dioxide CO₂ or carbon monoxide COgas as the second raw material gas is supplied from the cylinder 12A, sothat the ozone generator can be obtained in which the ozone generationefficiency can be adequately raised by the simple raw material supplystructure, and the generation of a by-product such as NOx can besuppressed.

Embodiment 7

Embodiment 7 of this invention will be described with reference to FIG.14. FIG. 14 is a block diagram showing a structure of a gas system inthe embodiment 7.

In FIG. 14, a raw material gas 25 is supplied from a first, second andthird raw material gas dedicated gas cylinder 103 for supplying a first,second and third raw material gas in which a trace quantity of nitrogenor nitrogen dioxide N₂O₄ (NO₂) (second raw material gas) and noble gas(third raw material gas) such as argon are mixed to oxygen (first rawmaterial gas) having a purity of 99.99% or more. The other structure isthe same as FIG. 1 in the embodiment 1.

It is known that also in the noble gas, such as helium, argon or xenon,or carbon dioxide, ultraviolet light of 300 to 400 nm is emitted bysilent discharge. Thus, it has been experimentally confirmed that theozone generation efficiency η is increased.

By ultraviolet light emitted by each of the nitrogen dioxide as thesecond raw material gas and the noble gas, the oxygen molecule can bedissociated and, or the oxygen molecule can be dissociated by thephotocatalyst of the nitrogen dioxide, the nitrogen dioxide isregenerated by the reaction of the reaction equations R71 and R81 in thedischarge space part, and the ozone is generated.

When the third raw material gas is made the noble gas or carbon dioxide,the addition quantity of the nitrogen compound to the ozone generator300 can be made very small, and accordingly, the generation quantity ofNOx as the nitrogen by-product other than ozone by silent discharge isalso lowered, the nitric acid cluster of moisture and NOx can also bedecreased, and the precipitation of metal impurity by nitric acid at theozone outlet part is also decreased. Thus, a further clean ozone gas canbe provided.

As stated above, by forming the dedicated cylinder for the ozonegenerator, there are obtained effects that the raw material gas supplysystem can be simplified, and the cost of the raw material gas can bereduced.

Besides, when the second raw material gas and the third raw material gasare added to the high purity oxygen, and further the nitrogen gas isadded, the addition quantity of nitrogen can be variably controlled bythe ozone Regenerator and the ozone generation performance such as ozoneconcentration can be made stabler.

According to the embodiment 7, since the first, second and third mixturegas dedicated raw material gas cylinder 103 for supplying the first,second and third mixture gas is constructed, the ozone generator can beobtained in which the ozone generation efficiency can be adequatelyraised by the simple raw material supply structure.

The ozone generator of the embodiments 1 to 7 includes a first electrode301 a, a second electrode 301 b facing a main face of the firstelectrode 301 a to form a discharge area, a dielectric plate and aspacer for forming the discharge area between the first electrode 301 aand the second electrode 301 b, a first raw material gas supply unit forsupplying a high purity oxygen gas as a first raw material gas, a secondraw material gas supply unit for supplying a second raw material gas asan oxide compound gas or capable of generating an oxide compound gas,and a third raw material gas supply unit for supplying a third rawmaterial gas which is excited by discharge and generates excited lightto dissociate the oxide compound gas or to excite the oxide compound gasto accelerate dissociation of the oxygen gas, wherein an AC voltage isapplied between the first electrode 301 a and the second electrode 301 bfrom a power supply to inject discharge power to the discharge area,specified quantities of the raw material gases by the first to the thirdraw material gas supply units are supplied to a space where thedischarge is generated between gaps of the discharge area, and an ozonegas is generated.

Then, by the oxygen gas as the first raw material gas, the second rawmaterial gas, the third raw material gas, and the discharge, i) theoxide compound gas exists, ii) excited light having a predeterminedlight wavelength is generated by excitation of the gas atom or moleculeof the third raw material gas by the discharge, iii) the oxygen atom (Oatom) is generated by the chemical reaction of the oxide compound gasand the excited light, or the photocataltic action of the oxide compoundgas, and iv) by the binding action with the raw material oxygen gas (O₂molecule), and by the circulation cycle of the discharge and gaschemical reaction action of i), ii), iii) and iv), or by thephotocataltic action of the oxide compound gas itself, ozone with aconcentration of approximately 10 g/m³ (4667 ppm) or more can begenerated, and this ozone can be extracted, and accordingly, the ozonegeneration efficiency can be adequately raised. Besides, there areeffects that in order to obtain specified ozone, the discharge power canbe made low, the ozone generator and the ozone power supply becomecompact, and the running cost becomes low. Besides, there are effectsthat the nitrogen additive rate of the raw material gas can also belowered, the generation quantity of NOx gas other than the ozone gasgenerated in the ozone generator can also be lowered, the precipitationof metal impurity by the ozone gas extraction pipe and nitric acid canalso be suppressed, and a clean ozone gas can be extracted.

Embodiment 8

Embodiment 8 of this invention will be described with reference to FIG.15. FIG. 15 is a block diagram showing a structure of a gas system inthe embodiment 8.

In the embodiment 8, as shown in FIG. 15, a mixture gas in which a tracequantity of noble gas, such as argon Ar or helium, as a third rawmaterial gas is added to high purity oxygen (first raw material gas) issupplied as a raw material gas 25 from a dedicated gas cylinder 101 toan ozone generator 300. Further, in a dielectric 302A, made of ceramic,glass or the like, of the ozone generator 300, a photocataltic componentof tungsten oxide WO₃, chromium oxide cro₂, iron oxide Fe₂O₃ or titaniumoxide TiO₂ is made to be contained in the ceramic or glass constitutingthe dielectric 302A.

When the photocataltic material component such as tungsten oxide WO₃ orchromium oxide CrO₂ is contained in the dielectric 302A, made ofceramic, glass or the like, of the ozone generator 300, ultravioletlight of from 300 to 400 nm of discharge light by the noble gas such asAr is irradiated onto the photocataltic surface of tungsten oxide WO₃ orthe like, this ultraviolet light is absorbed by the tungsten oxide orthe like, and the photocataltic material such as the tungsten oxide isbrought into an excited state. When the oxygen gas is adsorbed to thephotocataltic surface in the excited state, transfer of energyequivalent to light (ultraviolet rays of 130 nm to 200 nm) capable ofdissociating the oxygen gas is performed when the photocataltic materialis returned from the excited state to the ground state, and the oxygengas is dissociated into the oxygen atoms. Thus, the photocatalticmaterial such as the tungsten oxide WO₃ functions as the second rawmaterial gas. Ozone is generated by triple collision (reaction equationR2) of the oxygen atom, the oxygen molecule and a third material.

As the photocataltic material, it is effective to cause different kindsof materials to be contained in the dielectric 302A or the electrode 301at the same time. This is because the absorption light of the dischargelight (ultraviolet light of 300 to 400 nm) from the noble gas, which isabsorbed by the photocatalytic material to cause the excited state,varies according to the photocataltic material, and it appears that thedifferent kinds of photocataltic materials can be effectivelytransferred into to the excited state by the same quantity of dischargelight.

Besides, the photocataltic material may be a material, such as tungstenmaterial W, which easily becomes tungsten oxide WO₃ by the oxygen gas.

In this embodiment 8, the photocataltic component, such as tungstenoxide, chromium oxide, titanium oxide or iron oxide, is made to becontained in the dielectric 302A. Although a film of the photocatalyst,such as tungsten oxide, chromium oxide, titanium oxide or iron oxide,may be formed on the discharge surface of the dielectric, thephotocataltic film is degraded by sputtering from the silent discharge,the ozone performance is degraded with the lapse of operation time, andthe lifetime of the ozone generator is shortened.

Thus, like this embodiment, it is preferable to adopt the structure thatthe photocataltic component is contained in the dielectric 302A.

The ozone generator of the embodiment 8 includes a first electrode 301a, a second electrode 301 b facing the first electrode 301 a to form adischarge area, the dielectric 302A in the discharge area between thefirst electrode 301 a and the second electrode 301 b, a first rawmaterial gas supply unit for supplying a high purity oxygen gas as afirst raw material gas, a photocatalytic material or a material capableof being transformed into a photocatalyst, provided in the dielectric orthe electrode in the discharge area, and a third raw material gas supplyunit for supplying a third raw material gas which is excited bydischarge and generates excited light to excite the photocatalyticmaterial to accelerate dissociation of the oxygen gas, wherein an ACvoltage is applied between the first electrode 301 a and the secondelectrode 301 b from a power supply to inject discharge power to thedischarge area, a specified quantity of the raw material gas 25 by thefirst and third raw material gas supply unit is supplied to a spacewhere the discharge is generated between gaps of the discharge area, andan ozone gas is generated.

When the dielectric 302A or the elect rode 301 provided in the dischargearea is made to contain the photocataltic material, by the oxygen gas asthe first raw material gas, the third raw material gas, thephotocataltic material, and the discharge, i) excited light with apredetermined light wavelength is generated from the noble gas by thedischarge light, ii) an oxygen atom (O atom) is generated from theoxygen gas by the photocataltic reaction of the photocataltic materialof the dielectric 302A or the electrode 301 and the excited light, ozonewith a concentration of approximately 10 g/m³ (4667 ppm) or more isgenerated, and this ozone can be extracted. Thus, the ozone generatorcan be obtained in which the ozone generation efficiency can beadequately raised by the simple gas supply structure. In this embodiment8, since nitrogen or nitrogen dioxide gas is not used, the clean ozonegenerator can be obtained in which NOx of a by-product gas is notgenerated.

Embodiment 9

Embodiment 9 of this invention will be described with reference to FIG.16. FIG. 16 is a block diagram showing a structure of a gas system inthe embodiment 9.

In the embodiment 9, as shown in FIG. 16, by combination of a highpurity oxygen (first raw material gas) cylinder 10 and an auxiliarycylinder 2000 in which nitrogen dioxide or the like is added to a noblegas, a high purity oxygen gas as the first raw material gas and anauxiliary raw material gas made of nitrogen dioxide NO₂ (second rawmaterial gas) and a base noble gas (third raw material gas) such asargon are made a raw material gas 25 and are supplied to an ozonegenerator 300. A dielectric 302A, made of ceramic or glass, of the ozonegenerator 300 is made to contain a photocataltic component (functioningas a second raw material gas) such as tungsten oxide WO₃ or chromiumoxide CrO₂. As the raw material gas, the auxiliary raw material gas hasonly to be added to the oxygen, and there is an effect that the cost ofthe dedicated cylinder of the raw material gas or pipe system equipmentcan be reduced.

The ozone generator of the embodiment 9 includes a first electrode 301a, a second electrode 301 b facing the first electrode 301 a to form adischarge area, the dielectric 302A in the discharge area between thefirst electrode 301 a and the second electrode 301 b, the first rawmaterial gas supply unit 10 for supplying the oxygen gas as the firstraw material gas, a photocatalytic material or a material capable ofbeing transformed into a photocatalyst, provided in the dielectric 302or the electrode in the discharge area, a second gas supply unit forsupplying a second raw material gas as an oxide compound gas or capableof generating an oxide compound gas, and a third raw material gas supplyunit for supplying a third raw material gas which is excited bydischarge and generates excited light to excite the photocatalyticmaterial and the oxide compound gas to generate an oxygen atom, whereinan AC voltage is applied between the first electrode 301 a and thesecond electrode 301 b from a power, supply to inject discharge power tothe discharge area, specified quantities of the raw material gases bythe first to the third raw material gas supply units are supplied to aspace where the discharge is generated between gaps of the dischargearea, and an ozone gas is generated.

When the dielectric 302A or the electrode 301 provided in the dischargearea is made to contain the photocataltic material, by the oxygen gas asthe first raw material gas, the second and the third raw material gasesin the auxiliary gas, the photocatalytic material, and the discharge, i)the oxide compound gas exists, ii) excited light having a predeterminedlight wavelength is generated from the noble gas in the auxiliary rawmaterial gas by discharge light, and iii) by chemical reaction orphotocatalytic reaction of the oxide compound gas, the photocatalyticmaterial and the excited light, the oxygen atom (O atom) is generatedfrom the nitrogen dioxide or oxygen gas, ozone with a concentration ofapproximately 10 g/m³ (4667 ppm) or more can be generated, and thisozone can be extracted. Accordingly, the ozone generator can be obtainedin which the ozone generation efficiency can be adequately raised by thesimple gas supply structure.

In the embodiment 9, the dielectric in the ozone generator or thedischarge surface of the electrode is formed of the photocatalticmaterial, and when ozone is generated for a long time by thephotocataltic material of the discharge surface, the discharge surfaceof the photocataltic material is degraded or becomes dirty, and thegeneration capacity of ozone is lowered by the time-varying degradation,and the lifetime is shortened. However, when the dielectric in the ozonegenerator or the discharge surface of the electrode is made of thephotocataltic material, and the oxide compound gas (second raw materialgas) is added to the raw material gas, the oxide compound gas itself hasthe capacity to generate ozone, and the apparatus can be obtained inwhich ozone can be more stably generated, and the lifetime is long.

Embodiment 10

Embodiment 10 of this invention will be described with reference to FIG.17. FIG. 17 is a block diagram showing a structure of a gas system inthe embodiment 10.

In the embodiment 10, as shown in FIG. 17, a mixture gas in which atrace quantity of nitrogen N₂ or nitrogen dioxide NO₂ gas as a secondraw material gas is added to high purity oxygen (first raw material gas)is supplied from a dedicated gas cylinder 101, a noble gas such as argonis supplied from a gas cylinder 20, and these gases are supplied as araw material gas 25 to an ozone generator 300. In a dielectric 302, madeof ceramic, glass or the like, of the ozone generator 300, aphotocataltic material component of tungsten oxide WO₃, chromium oxideCrO₂ titanium oxide TiO₂ or iron oxide Fe₂O₃ is made to be contained inthe ceramic, glass or the like. This also has the same effect as theembodiment 9.

Embodiment 11

Embodiment 11 of this invention will be described with reference to FIG.18. FIG. 18 is a block diagram showing a structure of a gas system inthe embodiment 11.

In the embodiment 11, as shown in FIG. 18, by combination of a highpurity oxygen (first raw material gas) cylinder 102 and an auxiliarycylinder 2000 in which nitrogen dioxide or the like is added to a noblegas, a high purity oxygen gas as a first raw material gas and anauxiliary raw material gas made of nitrogen dioxide NO₂ and a base noblegas such as argon are supplied as a raw material gas 25 to an ozonegenerator 300, and a tungsten material 301C is bonded to a dielectric302, made of ceramic, glass or the like, of the ozone generator 300 andto a discharge surface of an electrode member 301 b made of SUS as theother electrode. When the tungsten member 301 is bonded so as toconstitute the electrode, the oxygen gas is made to flow, and ozone isgenerated, a tungsten oxide film WO₃ is formed on the discharge surfaceof the tungsten member 301C, and the tungsten oxide film WO₃ becomes aphotocatalyst. The photocatalyst has the same function as thephotocataltic material of the embodiment 9. Besides, also when atitanium member 301C is bonded to the discharge surface of the electrodemember 301 b, a titanium oxide film TiO₂ as a photocatalyst is similarlyformed and is effective. As the raw material gas, the auxiliary rawmaterial gas has only to be added to oxygen, and there is an effect thatthe cost of the dedicated cylinder of the raw material gas or pipesystem equipment can be reduced.

Besides, as the photocataltic material, although WO₃ material, CrO₂material, TiO₂ material or Fe₂O₃ material has been indicated, as thephotocataltic material, another metal semiconductor material orferroelectric material also has a photocataltic effect, and also whenthe metal semiconductor material or the ferroelectric material isadopted, high concentration ozone can be efficiently generated.

When the photocataltic film formed on the surface of the dielectric 302,made of ceramic, glass or the like, of the ozone generator 300 or theelectrode surface, is formed of two or more different photocatalticmaterials, not the single photocataltic material, the photocataltic filmcan absorb discharge light of plural wavelengths. As a result, thephotocataltic film is brought into the excited state more efficiently,dissociation of oxygen can be efficiently performed, the ozonegeneration quantity is increased, and high concentration ozone can beobtained.

Besides, according to the embodiment, in the structure of the foregoingdescription, the second raw material gas is one of nitrogen dioxide,nitrogen monoxide, nitrogen, carbon dioxide, and carbon monoxide, andthe second raw material gas of from 0.2 ppb to several hundred ppm isadded to the oxygen gas, so that ozone with a concentration ofapproximately 10 g/m₃ (4667 ppm) or more can be generated.

Besides, according to the embodiment, in the structure of the foregoingdescription, the third raw material gas is one of noble gas, such ashelium, neon, argon or xenon, nitrogen monoxide, nitrogen dioxide, andcarbon dioxide, and the third raw material gas of from several hundredppm to 50000 ppm is added to the oxygen gas, so that ozone with aconcentration of approximately 10 g/m³ (4667 ppm) or more can begenerated.

Here, with respect to the foregoing embodiments 1 to 11, a supplementaldescription will be made with reference to FIGS. 19 to 28.

The embodiment of the invention does not aim at suppressing thetime-varying concentration reduction of the generated ozone gas, butaims at finding a new system to obtain high concentration ozone by anozone generator, realizing an apparatus based on that, and raising theefficiency of extractable ozone to realize a compact generator and ozonegenerating system.

Besides, as a supplemental result from the former object, another objectis to provide an ozone generator in which a nitrogen additive rate issuppressed to several hundred ppm or less, the total quantity of NOxsecondary gas, such as N₂O₅, other than ozone gas by discharge, and theby-product such as a nitric acid cluster is suppressed to a very smallgeneration quantity as compared with the conventional nitrogen additiverate, the generator is compact (predetermined discharge area or less),and a high concentration ozone gas with a high flow rate and aconcentration of 200 g/m³ (93333 ppm) or more can be obtained at anozone generation quantity of 24 g/h or more.

Besides, still another object is to provide a stabilized raw materialgas by causing the raw material gas mainly containing the oxygen gas forthe ozone generator, which can achieve the two former objects, to becontained in a dedicated cylinder.

FIG. 19 is a view in which an ozone concentration characteristic in acase where nitrogen dioxide is added to a raw material gas, and an ozoneconcentration characteristic in a case where a TiO₂ film of metal oxideas a photocatalyst is formed on an electrode surface in an ozonegenerator.

The drawing shows ozone concentration characteristics with respect todischarge power W/Q injected per unit flow rate, a characteristic 1900Cindicates a characteristic in a case where nitrogen dioxide NO₂ of 10ppm is added to oxygen of a raw material gas, a characteristic 1900Dindicates a characteristic in a case where a raw material gas is madeonly an oxygen gas and a TiO₂ film is formed on the electrode surface ofa discharge part of the ozone generator, a characteristic 1900Bindicates a characteristic in a case where an electrode film of theozone generator is made a Tio₂ film, and an argon gas is added to anoxygen gas to prepare a raw material gas, and a characteristic 1900Aindicates a characteristic in a case where the electrode surface of theozone generator is made a TiO₂ film, and nitrogen dioxide NO₂ is addedto an oxygen gas to prepare a raw material gas. As is understood fromthe drawing, with respect to the ozone concentration characteristic,although sufficient ozone can be generated in any condition, the ozoneconcentration characteristic (1900D) in the case of the combination ofthe Tio₂ electrode and the oxygen gas is worst. This is because insilent discharge using only the oxygen, the light quantity ofultraviolet light of 300 to 400 nm to photoexcite the TiO₂ film as thephotocataltic material, which is emitted by discharge, is low, so thatthe TiO₂ film can not be sufficiently photoexcited, and does notsufficiently function as the photocataltic material.

Next, when the argon gas or nitrogen dioxide is added to the TiO₂electrode and the oxygen gas (1900B, 1900A), a high concentration notlower than an ozone concentration of 300 g/m³ is obtained under thecondition that the unit injection power W/Q is 300 or more, and themaximum becomes about 380 g/m³. This is because the nitrogen dioxide orargon gas can sufficiently emit the ultraviolet light of 300 to 400 nmby silent discharge, so that TiO₂ of the photocataltic material ornitrogen dioxide NO₂ itself can be photoexcited, and the oxygen gas(oxygen molecule) can be sufficiently dissociated into the oxygen atomsby the photoexcited TiO₂ or nitrogen dioxide N₂, and as a result, highconcentration ozone can be obtained. Besides, when the unit injectionpower W/Q is 200 or less, unless the nitrogen dioxide is added to theraw material gas at the TiO₂ electrode, the ozone concentrationcharacteristic eventually becomes low. That is, this means that when thenitrogen dioxide is added to the raw material gas, the ozone generationefficiency becomes higher than that of the case of the TiO₂ electrode.It can be construed that this cause is such that under the condition oflow W/Q, the ultraviolet light of 300 to 400 nm emitted from thedischarge does not effectively impinge on the electrode surface, and thedissociation efficiency of the oxygen gas is low. On the other hand,since the nitrogen dioxide as the photocataltic material is gas itself,the ultraviolet light of 300 to 400 nm emitted by the silent dischargeeffectively impinges, the dissociation efficiency of the oxygen gasbecomes higher than that of the photocataltic material of the electrodesurface, and the ozone generation efficiency also becomes high.

Incidentally, although not shown, it has been confirmed that even when anoble gas such as a He gas instead of an argon gas is added as the noblegas, the ultraviolet light of 300 to 400 nm can be emitted by silentdischarge, and it contributes to the role to raise the generation ofozone. Besides, since the He gas has a molecular weight smaller than theargon gas, the diameter of one discharge column of the silent dischargebecomes large, and it has an effect to stabilize the discharge.

Further, although it has been shown that the TiO₂ film is formed on theelectrode surface of the generator, when a tungsten electrode, or aniron or stainless electrode is used, a tungsten oxide film WO₃ or aferric oxide film Fe₂O₃ is formed on the discharge surface, the tungstenoxide film WO₃ or the ferric oxide film Fe₂O₃ has the photocatalticaction, and the ozone concentration characteristic slightly higher thanthat of TiO₂ is indicated. The energy value of a band gap forphotoexciting the tungsten oxide film WO₃ and the ferric oxide filmFe₂O₃ is 2.8 eV and 2.2 eV, respectively, and is small as compared withthe energy value (3 eV, 3.2 eV) of the band gap for photoexciting TiO₂.Thus, with respect to the wavelength of the ultraviolet light forphotoexcitation, although the ultraviolet light of 300 to 400 nm isneeded in the case of the TiO₂ film, in the case of WO₃, the light of330 to 470 nm is sufficient, and in the case of Fe₂O₃, the light of 564nm is sufficient, and even the discharge light of the silent dischargeof the oxygen gas itself and the visible light can sufficiently causephotoexcitation, and there is an effect that ozone generation can alsobe effectively performed.

FIG. 20 shows ozone concentration characteristics with respect to thequantity of nitrogen or nitrogen dioxide contained in a raw materialgas.

Systems enabling generation of ozone include three systems: i) a system(characteristic 20002A) in which nitrogen is added to the raw materialgas, ii) a system (characteristic 20000A) in which nitrogen dioxide isadded to the raw material gas, and iii) a system (characteristic 20001A)in which a discharge part in the generator is formed of a photocatalystsuch as WO₃, Fe₂O₃ or TiO₂, and in the drawing, ozone concentrationcharacteristics of the respective systems are indicated by solid lines(characteristic 20002A), (characteristic 20000A) and (characteristic20001A).

Besides, broken lines (characteristic 20002B), (characteristic 20000B)and (characteristic 20001B) indicate ozone concentration characteristicsin the case where an argon gas is further added to the raw material gasin the above three systems enabling the ozone generation.

Besides, the drawing shows a rough allowable value of nitrogen (NOxquantity) contained in a cylinder itself in the high purity cylindersuch as an oxygen cylinder of a raw material gas. With respect to theillustrated cylinders having respective purities, an experimental datavalue lower than that has a large error and is a value which can not beevaluated much.

As shown in FIG. 20, in the respective systems, when a specifiedquantity for more of nitrogen or nitrogen dioxide is added, even if theargon gas is added, the ozone concentration is not raised. That is, theargon gas performs an auxiliary action useful to accelerate generationin the case where the quantity of the nitrogen gas or nitrogen dioxideis small.

Further, in the newest “etching apparatus of an oxide film by ozone” or“ozone water washing of a wafer or the like”, a high ozone concentrationof 200 g/m³ or more is needed, and with respect to the ozone generationquantity, there is a request for an ozone generator having an ozonecapacity of several tens g/h or more on an economic basis in productionof the user side, and further, in a semiconductor manufacture apparatus,an apparatus with little reaction poisonous substance such as nitricacid has been needed.

FIG. 21 shows an ozone reaction ratio characteristic with respect toozone concentration when the reaction degree at an ozone concentrationof 100 g/m³ is made 1 (standard). As shown in FIG. 21, in the processingapparatus using the ozone gas, when the ozone gas with a highconcentration of 200 g/m³ or more is supplied, a general reaction speedis increased, and the processing efficiency is greatly increased.

Besides, FIG. 22 shows an example of a concentration characteristic ofozone concentration and concentration of ozone water in an apparatus forforming the ozone water by causing ozone gas to permeate into purewater. In FIG. 22, in the ozone water production apparatus, the ozonegas with a high concentration of 200 g/m³ or more is needed in order toobtain the ozone water of approximately 70 mg/L or more.

In the embodiment, an ozone generator 300 shown in FIG. 23 is of a typein which a both-sided electrode can be cooled and is constructed by agap length of 0.1 mm and a discharge area of about 750 cm². Whiledischarge power W up to about 2000 W was injected from an ozone powersupply, ozone concentration characteristics in the case where nitrogenwas added to high purity oxygen were thoroughly examined on experiment.

The ozone concentration characteristics were measured in the case where,as the nitrogen additive rate, 1) only high purity oxygen was used, 2) anoble gas of high purity oxygen was added, 3) nitrogen of 100 ppm wasadded, 4) nitrogen of 300 ppm was added, 5) nitrogen of 500 ppm wasadded, 6) nitrogen of 1000 ppm was added, and 7) nitrogen of 10000 ppmwas added.

FIGS. 24, 25 and 26 show examples of the results.

Besides, FIG. 27 shows characteristics of an injection power W/Q—ozoneconcentration C with respect to unit gas quantity in a case of nitrogenadditive rate of 1% (10000 ppm) and in a case of 0.05% (500 ppm). W(W)denotes discharge injection power, and Q(L/mim) denotes raw material gasflow rate. Tangential lines of these characteristics at lowconcentration (region where ozone loss can be neglected) are indicatedby broken lines.

The inclination of this broken line indicates the ozone generationefficiency η in principle, and indicates the ozone generation weight inthe case where electrical energy of 1 J is injected. That is, the unitof the ozone generation efficiency η is (mg/J).

Experimental characteristics concerning the relation between thenitrogen additive rate γ and the ozone generation efficiency η wereobtained, and the result is as shown in FIG. 28, and the approximateexpression is as follows:

approximate expression η=0.004310 g(γ)+0.033 [mg/J].

From this result, a remarkable result was obtained, that is, when thenitrogen additive rate y was 0%, the ozone generation rate TI was almost0 mg/J.

FIG. 24 shows the ozone concentration characteristic with respect to theinjection power in the case where only high purity oxygen gas is usedand the cases where the argon gas and the xenon gas are added.

With respect to the ozone concentration 290 g/M³ at 2000 W obtained inFIG. 25, in FIG. 24, in any raw material gases, only the ozoneconcentration of 10 g/m³ was obtained, and the separate additions of theargon gas and the xenon gas had little effect to raise the ozoneconcentration and the generation quantity. Here, although the cases ofthe argon gas and the xenon gas are shown as examples, the same resultwas obtained also for the addition of the noble gas such as helium orneon.

FIG. 25 shows ozone concentration characteristics 1700A, 1700B and 1700Cwith respect to the discharge power in the case where the nitrogenadditive rates are 0.01%, 0.1% and 1%.

Besides, a broken line 1700D indicates a condition of a discharge powerdensity of 0.25 W/cm² as low power density, and a broken line 1700Eindicates a condition of a discharge power density of 3 W/cm² as highpower density.

FIG. 26 shows the reduction ratio of the ozone concentration in a caseof nitrogen additive rate of 0.1% with respect to discharge powerdensity in the case where the ozone concentration characteristic of acase of a nitrogen additive rate of 1% is made 100%, and the ozoneconcentration characteristic of a case of a nitrogen additive rate of0.01% is made 0% (characteristic 1800A).

From this drawing, in the low power density of 0.25 W/cm², the ozoneconcentration is about 13% as compared with the concentration in thecase where nitrogen of 1% is added, and at the high power density of 3W/cm², the ozone concentration is reduced to about 86% as compared withthe concentration in the case where nitrogen of 1% is added.

That is, there is obtained a strain result that even if the nitrogenaddition quantity is the same, the cause of the reduction of the ozoneconcentration is different between the case of the high power densityand the case of the low power density.

From this result, the existence quantity of a by-product relating to thenitrogen gas in the discharge part is compared between the case of thehigh power density and the case of the low power density. Then, it hasbeen understood that at the high power density, the quantity of thenitrogen gas is very low, and the quantity of the oxide compound gas bydischarge, such as nitrogen dioxide, is large. On the contrary, it hasbeen ascertained that at the low power density, since the dischargepower is small, most of the gas is the nitrogen gas, and the quantity ofthe oxide compound gas such as nitrogen dioxide is small.

Then, at the low power density, as compared with the case of nitrogenaddition of 1%, in the case of nitrogen addition of 0.1%, ozoneconcentration substantially corresponding to the ratio of the nitrogenaddition quantity is merely obtained. At the high power density, theresult is such that the ozone concentration does not depend on thenitrogen addition quantity much.

From the above experimental result, it has been understood that twofactors exist as the factor contributing to the ozone generation ofsilent discharge.

That is, it has been found that the first factor is due to the factor ofnitrogen itself, and the second factor is due to the quantity of theoxide compound.

With respect to the factor of the nitrogen itself, from furtherexamination of discharge excited light, it has been understood that thenitrogen gas emits ultraviolet light of approximately 300 nm.

Besides, from the examination of light dissociation of the oxygen gasmolecule and nitrogen dioxide as the oxide compound gas, it has beenunderstood that the nitrogen dioxide can be dissociated by ultravioletrays of 300 nm, and the oxygen atom can be generated by thermalcatalytic reaction action, however, the oxygen molecule can not bedissociated if vacuum ultraviolet light of about 130 to 245 nm is notused.

Further, it has been understood that in the oxide compound gas such asnitrogen dioxide, the energy band from the valence band to theconduction band in the molecule is larger than the energy band of metal,and when light of ultraviolet rays of about 300 nm is impinged on thisenergy band, nitrogen dioxide performs light absorption, and thenitrogen dioxide itself is excited, and when the excited nitrogendioxide is returned to the ground state, and when the oxygen gas (O₂molecule) exists in the atmosphere, high energy equivalent toultraviolet light for dissociating the oxygen molecule is released, andthere is an effect to dissociate the oxygen molecule (that is,photocataltic action).

From the above series of results, it has been understood that the factorcontributing to the ozone generation by nitrogen oxide is lightdissociation of the nitrogen oxide gas, and accelerating action ofdissociation of the oxygen gas (O₂ molecule) itself by the photocatalticaction of nitrogen oxide, and the oxygen atom is generated.

In the following, the examination result of ozone generation will bedescribed in more detail.

In the addition of only the high purity oxygen, and the separateaddition of the noble gas or the like, the ozone generation efficiency ηis approximately 0 mg/J, which basically overturns a conventional ozonegeneration mechanism which is expressed by following reaction equationsR1 and R2.

e+O₂

2O+e (dissociation of oxygen)  R1

O+O₂+M

O₃+M (ozone generation based on triple collision of oxygen atom andoxygen material)  R2

From the conclusion, the relation between nitrogen and ozone has beenexamined in detail, and the following inference has been obtained.

The dew point of the ozone generator is about −70 to −60, and theconcentration of existing moisture contained in the raw material gas isfrom 3 ppm to 10 ppm or more.

The wavelength of absorption light for dissociating the oxygen moleculehas a continuous spectrum of ultraviolet rays of from 130 to 245 nm, andthe excited light of the nitrogen gas is ultraviolet light of 300 to 400nm, and can not directly optically dissociate the oxygen molecule.

With respect to the mechanism for generating the ozone gas through thenitrogen additive rate, the only possibility of the excited light of thenitrogen gas is ultraviolet light of 300 to 400 nm.

Thus, a nitrogen compound capable of dissociating the ozone atom byultraviolet light of 300 to 400 nm was examined. As a result, it hasbeen confirmed that there are (1) a mechanism of light emission ofultraviolet light by discharge, and electrolytic dissociation of watervapor H₂O and the nitrogen molecule, and (2) an ozone generationmechanism by NO₂. Besides, there are (3) a generation mechanism ofnitric acid by NO₂ to suppress ozone generation, and (4) a mechanism ofozone decomposition of the generated ozone, and the four mechanismsoccur in the silent discharge space of the ozone generator, and theconcentration of ozone which can be extracted is determined.

(1) Light emission of ultraviolet+ light by discharge and electrolyticdissociation of water vapor H₂O and nitrogen molecule

N₂ +e

N₂ *+e

N₂+hν (310, 316, 337, 358 nm)

N₂*: excitation of nitrogen

ultraviolet light by nitrogen gas

H₂O+e

H+OH+e (electrolytic dissociation of water vapor)

N₂ +e

2N+e (electrolytic dissociation of nitrogen molecule)

(2-1) Generation mechanism of ozone by thermal catalytic chemicalreaction of NO₂

NO₂ +hν (295 to 400 nm)

NO+O(³P)  R6

H+O₂+M

HO₂+M  R71

HO₂+NO

OH+NO₂  R81

O(³P)+O₂+M

O₃+M  R2

The oxygen atom O(³P) is formed (reaction of R6) by the nitrogen dioxideNO₂ and ultraviolet light of approximately 300 nm by excitation ofnitrogen, and ozone is generated (reaction of R2) by triple collision ofthe generated oxygen atom O(³P) and the oxygen molecule O₂. The nitrogenmonoxide NO generated from the reaction result of R6 reacts with an HO₂radical generated at the reaction of R71 and the nitrogen dioxide NO₂ isregenerated (reaction of R81).

That is, during the time when the raw material gas passes through thesilent discharge space, the nitrogen dioxide NO₂ repeats the reactioncycle of R6→R71→R81→R6 and is regenerated.

Besides, the oxygen atom O(³P) simultaneously generated during the timewhen the raw material gas passes through the silent discharge space issubjected to the triple collision (reaction of R2) to the oxygenmolecule and the ozone gas is generated.

(2-2) Generation mechanism of ozone by photocataltic reaction of NO₂

NO₂ +hν (295 to 400 nm)

NO₂*  H1

NO₂*+O₂

2O(³P)+NO₂  H2

2O(³P)+2O₂+M

2O₃+M  R2

The nitrogen dioxide NO₂ becomes excited state NO₂* (reaction of H1) bynitrogen dioxide NO₂ and ultraviolet light of approximately 300 nm bydischarge light of argon or the like or discharge light of nitrogen. Theexcited NO₂* gives energy equivalent to dissociation energy of theoxygen molecule to the oxygen molecule to dissociate it into the oxygenatom O(³P), and the nitrogen dioxide itself is returned to NO₂ in theground state.

The ozone is generated (reaction of R2) by the triple collision of thegenerated oxygen atom O(³P) and the oxygen molecule O₂. NO₂ in theground state again becomes the excited state NO₂* by the ultravioletlight of approximately 300 nm by the discharge light.

That is, during the time when the raw material gas passes through thesilent discharge space, the nitrogen dioxide NO₂ repeats the reactioncycle of H1→H2→H1 and is regenerated.

Besides, the oxygen atom O(³P) simultaneously generated during the timewhen the raw material gas passes through the silent discharge space issubjected to the triple collision (reaction of R2) to the oxygenmolecule and the ozone gas is generated.

(3) Generation mechanism of nitric acid by NO₂

OH+NO₂+M

HNO₃+M  R9

The nitrogen dioxide NO₂ generates ozone, and at the same time, nitricacid HNO₃ is also generated (reaction of R9), the generation of theoxygen atom is suppressed, and the generation efficiency η of ozone islowered.

(4) Mechanism of ozone decomposition

e+O₃

O+O₂ +e (electron collision decomposition)  R3

O₃+heat T

O+O₂ (heat decomposition)  R4

O₃+N

O₂+N1 (decomposition of ozone by impurity)  R5

The ozone generated by the reaction of R2 is decomposed (reaction of R3)by electron collision in the silent discharge space, is decomposed byheat (reaction of R4), and is decomposed by an impurity such as NOx(reaction of R5).

Thus, the ozone which can be extracted from the ozone generator becomesas follows, and like the ozone concentration characteristic of FIG. 27,as compared with the ozone generation efficiency η characteristic(broken line), the saturated characteristic occurs.

extractable ozone concentration=(ozone gene ration quantity)−(ozonedecomposition quantity)=(R2−R9)−(R3+R4+R5).

Although the reaction of R3 is increased linearly with respect to theinjection power of the silent discharge, since the reactions of R9, R4and R5 are increased in a lamp function by the increase of injectionpower, they prevent high concentration ozone gas from being extracted.

In order to raise the extractable ozone concentration, as means forsuppressing the reactions of R3 and R4, it has been already proposedthat the extractable ozone concentration is raised by causing thedischarge gap length in the generator to have a short gap (0.1 mm orless), or by cooling the electrode surface.

Besides, in order to raise the extractable ozone concentration, withrespect to means for suppressing the reaction of R5, it has been alreadyclear to use a high purity raw material gas with an excellent dew point(−50° C. or lower).

However, means for increasing the ozone generation quantity in order toraise the extractable ozone concentration has not been considered atall.

The reason is that it has been interpreted that the ozone is generatedby dissociating the oxygen molecule through high energy electroncollision of discharge, and by performing the triple collision of theozone atom and the ozone molecule, and therefore, it has been consideredthat the high energy electron quantity is almost constant when thedischarge state is determined, and the ozone generation quantity can notbe changed.

Besides, it has been regarded that the generated ozone is excited by thesilent discharge and the ozone molecule O₃ becomes O₃*, the excitedozone molecule O₃* is returned to the oxygen molecule by electroncollision, and time-varying concentration reduction of the extractableozone concentration occurs.

It has been considered that the nitrogen gas is effective as means forsuppressing the time-varying concentration reduction.

However, from the experiments, it has been newly found experimentallythat when the high purity oxygen gas is injected in the state where theozone generator is sufficiently made clean and an impurity gas otherthan the high purity oxygen can be neglected, the reduction of the ozoneconcentration is not time-varying concentration reduction, but essentialconcentration reduction due to pure oxygen.

While the presently preferred embodiments of the present invention havebeen shown and described. It is to be understood that these disclosuresare for the purpose of illustration and that various changes andmodifications may be made without departing from scope of the inventionas set forth in the appended claims.

1-11. (canceled)
 12. An ozone generator, comprising: a first electrode;a second electrode facing the first electrode and defining a dischargearea; a first raw material gas supply unit for supplying oxygen as afirst raw material gas; a photocatalytic material located on adielectric substrate located in the discharge area or on the firstelectrode for absorbing light in a specified wavelength range, or amaterial transformed into a photocatalyst by a discharge; and a thirdraw material gas supply unit for supplying a third raw material gaswhich is excited by the discharge and generates excited light to excitethe photocatalytic material to accelerate dissociation of the oxygen,wherein an AC voltage is applied between the first electrode and thesecond electrode from a power supply to supply discharge power to thedischarge area, quantities of the raw material gases are supplied by thefirst, second and third raw material gas supply units to a space wherethe discharge is generated in the discharge area, any in which ozone isgenerated in response to the discharge.
 13. The ozone generatoraccording to claim 12, wherein the photocatalytic material is selectedfrom the group consisting of WO₃, CrO₂, FeO₃, TiO₂, ametal-semiconductor structure, and a ferroelectric material.
 14. Theozone generator according to claim 12, wherein the photocatalyticmaterial includes a plurality of different photocatalytic materials. 15.The ozone generator according to claim 12, wherein the third rawmaterial gas is selected from the group consisting of a noble gas,nitrogen monoxide, nitrogen dioxide, and carbon dioxide, and the thirdraw material gas is contained in the oxygen in a concentration of fromseveral hundred ppm to 50000 ppm.
 16. The ozone generator according toclaim 12, including a cylinder in which the third raw material gas isadded to the first raw material gas. 17-23. (canceled)